The invention relates to making a fiber structure woven as a single piece by three-dimensional (3D) weaving, in particular for fabricating a composite material part. One particular, but non-exclusive, field of application of the invention lies in making fiber structures for preforms of composite material parts for aircraft or aeroengines, in particular for airplane turbine engines.
In well-known manner, a composite material part may be obtained by making a fiber preform and by densifying the preform with a matrix. Depending on the intended application, the preform may be made of glass, carbon, or ceramic fibers, and the matrix may be made of an organic material (a polymer), of carbon, or of ceramic.
For parts that are relatively complex in shape, it is known to make a fiber structure or blank as a single piece by 3D or multiple-layer weaving, and to shape the blank in order to obtain a fiber preform that presents a shape that is close to the shape of the part that is to be fabricated.
In order to facilitate such shaping, and in order to avoid making incisions that result in yarns being cut and that lead to a reduction in mechanical strength, it is known to leave one or more non-interlinked zones within the fiber structure while it is being woven. Such non-interlinked zones may be obtained by locally omitting any interlinking of the layers of adjacent yarns, thereby making it possible to fold out portions of the fiber structure adjacent to the non-interlinked zones.
The making of composite material parts that are complex in shape from woven structures with non-interlinked zones is described in particular in documents WO 2010/061139 and WO 2010/103213.
Nevertheless, the shaping of a fiber structure by folding out portions that are separated by a non-interlinked zone can give rise to weakness at the end of the non-interlinked zone and to excessive levels of stress on the yarns that are subjected to stress while performing such shaping.